592 SUPPLEMENTARY REMARKS ON WINDS, ETC. 



NANTUCKET SHOALS.— These very dangerous shoals, the " Good- 

 win Sands " of the United States, lie immediately in the line of traffic of 

 the coasting trade. They reach for 38 miles S.E. of Nantucket Island, 

 with depths varying from 4 ft. to 10 fathoms over them, and are liable to 

 great alterations both in form and position. It must also be remembered 

 that many of these shoals are so far from land that no marks can be given, 

 beyond that afforded by the lightship on their South extremity. Unless 

 in case of necessity, no vessel should become entangled in this labyrinth, 

 for the currents and tides are here most devious, the weather thick at 

 times, and the more prominent shoals shown by tremendous breakers, 

 while others are only to be distinguished by ripplings, more or less strong, 

 according to the tide or current, or by a discoloration of the water. 



Tides. — The main body of the flood tide runs to the eastward, the ebb 

 to the westward. The currents always run across the line of directions of 

 the shoals, and are much more rapid during their passage. This makes a 

 near approach particularly dangerous on the side toward which the tidal 

 current is setting. The current is never still ; during what is called slack 

 water, the velocity is rarely less than one-half, sometimes more than 1 mile. 



